Atrial fibrillation is a common sustained cardiac arrhythmia and a major cause of stroke. This condition is perpetuated by reentrant wavelets propagating in an abnormal atrial-tissue substrate. Various approaches have been developed to interrupt wavelets, including surgical or catheter-mediated atriotomy. It is believed that to treat atrial fibrillation by radio-frequency ablation using a catheter, continuous linear lesions must be formed to segment the heart tissue. By segmenting the heart tissue, no electrical activity can be transmitted from one segment to another. Preferably, the segments are made too small to be able to sustain the fibrillatory process. A preferred technique for treating atrial fibrillation by radio-frequency ablation would be a “branding iron” approach, where a relatively long electrode can be held stationary in good contact with the heart wall while ablation is completed. In this way, a continuous transmural bum may be effected.
U.S. Pat. No. 5,800,428 to Nelson et al. discloses a radio frequency ablation catheter system having a flexible, tubular electrode for creating a continuous linear lesion. The tubular electrode is selectively extendable from the distal end of the catheter. The catheter further comprises mechanisms for remotely manipulating and extending the electrode. However, having an extendable electrode house in the catheter provides less degrees of freedom with respect to the shape, size and length of the tubular electrode. Moreover, the physician has to deal with additional moving and manipulatable parts, adding complexity to the procedure. Further, a retractable electrode can cause contamination because blood or coagulate on the electrode can be pulled into and entrapped inside the catheter. The entrapped coagulate can also affect the ability of the electrode to be further extended and retracted. Accordingly, it would be desirable to provide a catheter design having an electrode for creating linear lesions that overcomes these drawbacks.
U.S. patent application Ser. No. 10/199,525, entitled “Atrial Ablation Catheter and Method for Treating Atrial Fibrillation” discloses a catheter having an ablation assembly bent relative to the catheter body and comprising a generally-straight non-retractable tubular electrode formed of a material having shape-memory having at least one irrigation port through which fluid can pass from the inside to the outside of the electrode. Two pairs of ring electrodes are provided, one pair mounted distal to the tubular electrode and one pair mounted proximal to the tubular electrode, for mapping electrical information. All of these components create a relatively long electrode assembly, which can be difficult to maneuver within the tight confines of the atrium. It would therefore be desirable to shorten the length of the ablation assembly while maintaining the functionality.